In recent years, the rapid development of mobile equipment, typified by the cellular phone, the mobile computer, the videotape recorder with an integrated camera and so on, has increased the need for reduced size and weight, especially in batteries and electronic components. At the same time, the demand for an increase in battery power has increased research on size and weight reductions while increasing the energy density of the battery. In particular, research for lithium batteries has been increasing, and now, lithium batteries serve as a preferred power source for mobile equipment.
Batteries typically have a positive electrode and a negative electrode separated by an insulating separator; they are stored in a sealed metal container that includes an electrolytic solution.
The positive electrode of a lithium battery can be obtained by adding an electrically conductive material to a metallic oxide as a positive electrode active material. Lithium cobaltite (LiCoO2) or lithium manganate (LiMn2O4) may be used as the positive electrode active material, for example, and acetylene black (AB) or graphite may be used as the electrically conductive material. The negative electrode of the battery may be obtained by solidifying an active material such as a lithium titan composite oxide like lithium titanate (Li4Ti5O12), graphite or amorphous carbon with resin. The negative electrode is produced in a like manner by adding and mixing a binder such as polytetrafluoroethylene or polyvinylidene fluoride to the active material to form the slurry, and then molding the slurry to form into a certain shape of negative electrode such as a sheet. A non-woven or microporous film separator, of polyolefin fiber having a heat resistance temperature of approximately 150° C., is interposed between electrodes, and a suitable electrolytic solution is provided. One suitable electrolyte solution is described hereinafter.
In such a lithium battery, the charge-discharge voltage of the positive electrode is approximately 4 V, whereas the charge-discharge voltage of the negative electrode active material is around 0 V, so that a high discharge voltage of approximately 3.5 V is achieved.
In prior art FIG. 1, the hermetically sealed battery C has a positive electrode case 11 provided with a positive electrode 11a made, for example, of stainless steel, and the opposing metallic sealing plate 12 provided with a negative electrode 12a made, for example, of stainless steel, in a vessel formed by joining the rim of the positive electrode case 11 and the rim of the sealing plate 12 mutually caulking and with a gasket material 15, with an electrolyte contained in insulation sheet 14 sandwiched between the positive electrode 11a and the negative electrode 12a. Charging and discharging at the positive electrode 11a and the negative electrode 12a are performed via external connection terminal members E attached to the positive electrode case 11 and the sealing plate 12. Such a construction is discussed in Japanese Unexamined Patent Publication JP-A 2000-106195 which also discusses an electric double layer capacitor of similar construction.
Prior art FIG. 2 shows a flat-type solid electrolyte battery D that uses a solid electrolyte as a battery element. This structure has the upper and lower surfaces of a ceramic frame 16 sealed with a lid plate 17 and a bottom plate 18 to define a hollow portion having a solid electrolyte body 14, a positive electrode 11b and a negative electrode 12b. The electrodes are electrically connected respectively to the bottom plate 18 and the lid plate 17 on opposite sides of the solid electrolyte 14 in a sealed container. In the solid electrolyte battery D, metalized layers are formed on the upper and lower surfaces of the ceramic frame 16 in order to join the bottom plate 18 and the lid plate 17 to the ceramic frame 16 via a conductive material (not shown) such as silver (Ag) solder. The electric connecting terminal E is also provided. Such a construction is discussed in Japanese Unexamined Patent Publication JP-A 57-80656 (1982). Further, in Japanese Unexamined Patent Publication JP-A 2001-216952, in order to avoid the use of the electric connecting terminal E, there is disclosed a battery or an electric double layer capacitor comprising an active material used as a positive electrode and a negative electrode, an electrolyte and a container which receives them therein, wherein the container is composed of a recessed container and a sealing plate, a first electrode is led from an inner bottom surface of the recessed container to an outer bottom surface of the recessed container, and a second electrode is led from an upper surface of the recessed container to the outer bottom surface, thereby the outer bottom surface of the recessed container is connected to an electrode of an external electric circuit board.
The prior art attempts suffer from several problems such as electrolyte leakage, degrading, corrosion or deterioration of the case or container by newer high-performance electrolytic solutions, and difficult external connections. Additional prior art attempts at solving these problems are disclosed in Japanese Unexamined Patent Publications JP-A 2002-50551 and JP-A 2003-100569.